Flexible sealant composition

ABSTRACT

THIS INVENTION RELATES TO A FLEXIBLE SEALANT, CAPABLE OF SETTING IN THE ABSENCE OF A POLYMERIZATION CATALYST, COMPRISING AN ACRYLAMIDE MONOMER, A POLYFUNCTIONAL CROSSLINKING AGENT SUTH AS AN ALKYLIDENE BISACRYLAMIDE, A POLYOL CONTAINING AT LEAST THREE HYDROXY GROUPS SUCH AS GLYCEROL AND A DIOL SUCH AS ETHYLENE GLYCOL. THE SEALANT IS PARTICULARLY USEFUL IN GROUTING APPLICATIONS WHERE HIGH ELECTRICAL RESISTIVITY IS DESIRED AND MAY BE USED FOR STABILIZING SOIL, CONSOLIDATING LOOSE SAND, GROUTING AND BRIDGING OR PLUGGING OPENINGS OF VULGAR AND/OR FRACTURED FORMATIONS.

United States Patent ()flice 3,649,574 Patented Mar. 14, 1972 3,649,574FLEXIBLE SEALANT COMPOSITION Robert C. Cole, Duncan, Okla., assignor toHalliburton Company, Duncan, Okla. No Drawing. Filed Oct. 29, 1968, Ser.No. 771,631 Int. Cl. C08f 45/04, 45/18, 45/34 U.S. Cl. 260-17.4 R 9Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTIONUnderground explosions and especially nuclear explosions have recentlybeen carried out to study the characteristics of nuclear devices.Additionally, an underground explosion may be used to form a largeunderground cavity for storing materials such as natural gas and to meltand recover various materials which are normally mined by moreconventional techniques.

In order to place the explosive charge into the ground, a hole must bedrilled. The force of the shock wave is countered by filling the holewith gravel or a similar material. This stemming material is usuallyporous and does not prevent the escape of gases containing radioactivebyproducts of the nuclear explosion. Thus, in addition to the gravel, itis necessary to have a sealing material that will prevent the escape ofradioactive materials and yet be flexible enough to withstand the shockwave. The sealant must also be easy to remove so that access to theexplosion chamber can be readily obtained after the explosion hasoccurred.

The sealant should also be nonhydrocarbon so that it is inert topolyvinyl chloride and rubber which are used to insulate wires carryinginstrumentation from the surface of the earth down the hole and into thetest chamber. The sealant must be nonthermoplastic and must also havelow inflammability because high temperatures are encountered. It mustalso have thermal properties such that the exotherm from thepolymerization does not raise the temperature above 125 F. which wouldcause damage to the wires going through the sealant. Shrinkage must beat a minimum in order to preserve a tight seal. The gel time of thesealant must be long enough to allow for mixing and placement of theseal-ant and yet rapid enough so that there is not seepage into thelower gravel pack or bed. Finally, the sealant must have low galvanicaction and the electrical resistivity should be at least about 50,000ohmcentimeters to prevent absorbing of radio signals.

Normally, grouting or soil stabilizing compositions which might be usedas flexible sealants and for other subterranean uses are originally inthe liquid state and require a catalyst to cause the sealing compositionto gel or harden.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a flexible sealing material which does not require addition of acatalyst.

It is a further object of the present invention to provide a flexiblesealing material which will not rupture when subjected to a shock wave.

A further object is to provide a flexible sealing material which has ahigh electrical resistivity.

Another object of the present invention is to provide a flexible sealingmaterial which is inert to conventional wire insulation coverings.

Still another object of the present invention is to provide a sealing orgrouting material where a non-dehydrating grout is needed or desired.

Yet another object of the present invention is to provide a sealingmaterial for sealing joints in discharge lines, and drawdown tubes fromdams and other water reservoirs which are dry fora portion of the yearand wet for another portion; for sealing certain types of sewer jointgrouting; and, for sealing joints in manholes where the joints are abovethe water table for a portion of the year.

These and further objects of the present invention will be more readilyunderstood by reference to the description and examples which follow.

Briefly, the present invention comprises a flexible sealant comprisingan acrylamide monomer, a polyfunctional crosslinking agent such as analkylidene bisacrylamide, a polyol containing at least three hydroxylgroups such as glycerol and a diol such as ethylene glycol. It has beenfound that the presence of the polyol causes the composition to gelwithout the necessity of having a catalyst present in the composition.The resulting gelled composition provides a flexible sealant of highelectrical resistivity for underground formations.

DESCRIPTION OF PREFERRED EMBODIMENTS The flexible sealant of the presentinvention is obtained by polymerizing an acrylamide monomer in thepresence of a polyfunctional crosslinking agent and a polyol. Prior toadding the monomer and crosslinking agent to the poly- 01, both theacrylamide monomer and the crosslinking agent should be dissolved in adiol such as ethylene glycol. After addition of the polyol, theresulting mixture may be introduced into a cavtity to be sealed. In thecavity, the mixture will polymerize without the necessity of adding acatalyst.

The monomer used in the flexible sealant polymerizes, resutling ingelation of the fluid. It is important that the monomer be one whichexhibits hydrogen bonding in order to produce the necessary flexibilty.Especially suitable monomers are the acrylamide monomers described inKoch U.S. Pat. 3,223,163 and having the structure R o R 1 lg CH2 C N RIIwhere R is either H or CH R is either H or an alkyl group, and R" iseither H or an alkyl group. Although acrylamide and substitutedacrylamides are preferred, many other monomers are suitable inpracticing the present invention. Other monomers include those listed inRoth U.S. Pat. 2,801,985, Morgan U.S. Pat. 2,801,984 and Rakowitz U.S.Pat. 2,940,729, which do not ionize significantly in a polyol solventand which are soluble in a polyol solvent. The disclosures of the fourabove-mentioned patents are incorporated herein by reference. Ingeneral, the amount of monomer may vary from about 2% to about 25% byweight of the mixture.

In order to form a gel, it is necessary to include a crosslinker for themonomer. In general, any polyfunctional monomer such as polyethyleniccompounds may be used. A preferred crosslinking material isN,N-methylenebisacrylamide. Other crosslinking materials which may beused in place of the N,N'-methylenebisacrylamide are disclosed in RothU.S. Pat. 2,801,985, Morgan U.S. Pat. 2,801,984 and Rakowitz U.S. Pat.2,940,729. In addition, other crosslinking materials such as triallylphosphate, diallylfumarate, etc., wherein there are seven or more atomsin the chain between the double bonds of these polyfunctionalcrosslinking agents, may be employed. Additionally, other compoundswhich do not fit into this category may also be used. Typical of suchcompounds are N, N-diallylacrylamide. Such compounds are disclosed inMcLaughlin US. Pat. 3,334,689, the disclosure of which is herebyincorporated into this application by reference. The amount ofcrosslinking agent should be sufiicient to form a gel and normally willvary from about 0.1% to about 10% by weight based upon the weight of themonomer used. Preferably, the amount of crosslinking agent should varyfrom about 1% to about 5% by weight based upon the weight of themonomer.

Another component of the composition of this inven tion is a diol. Thediol is used to dissolve the monomer and crosslinking agent.Additionally, the diol makes the mixture inert to rubber and otherinsulating materials for electrical wires which may pass through theflexible sealant and increases the electrical resistance of the sealant.The preferred diol is ethylene glycol but other diols such as diethyleneglycol, triethylene glycol, and other glycols in this series topolyethylene glycol, propylene glycol, 1,4- butene glycol, etc. may beused. The diol is present in an amount such that the weight ratio ofdiol to monomer is between about 1:1 to about 5:1. Preferably, the diolto monomer ratio is about 2: 1.

To the solution of monomer and crosslinking agent in diol is added apolyol containing at least three hydroxyl groups. The primary functionof the polyol in this composition is to cause the acrylamide monomer andcrosslinker to gel. This gel promoting function of the polyol isunexpected and it is not yet known exactly in what manner the polyolfunctions to promote gelling. The preferred polyol is glycerol. However,other polyols containing at least three hydroxyl groups such as those inthe homologous series, glycerol through the hexane hexols, e.g.,sorbitol and mannitol, may be used. In addition to promoting gelation ofthe acrylamide monomer, the polyol also acts to make the sealantcomposition inert to rubber and it increases the electrical resistivityof the sealant. The weight ratio of polyol to acrylamide monomer mayvary from about 2:1 to about 20:1 with the preferred ratio being about:1.

As previously indicated, it is important that the monomer andcrosslinking agent be first dissolved in a diol before addition of thepolyol. If the polyol is added directly to the mixture of monomer ancrosslinking agent, gelation will be essentially instantaneous and thusdifficult to control. Of course, in some applications, a rapid gellingtime is desirable. The presence of the diol apparently delays thepromoting action of the polyol. In placing the grouting fluid or sealantof this invention, the polyol may be added to the composition prior toinjection below the surface of the earth. On the other hand, a twostreammethod of placement may be used wherein one stream containing themonomer and crosslinking agent dissolved in diol is introduced below thesurface of the earth into the area which is to be sealed or consolidatedand a second stream containing the polyol is introduced into the samearea. Then, if adequate mixing occurred, a suitable sealant would beobtained.

An important use of the flexible sealant is as a part of the stemmingmaterial filling the access shaft of a chamber in which a high shockwave and pressure are generated. A typical use is in the access shaftfor an underground explosion such as an underground nuclear explosion.Underground nuclear explosions may be used to determine the explosivecharacteristics of the nuclear device to form a large undergroundcavern, or in connection with recovery of underground oil, minerals,etc. The test chamber in which the explosion occurs is usually connectedto the surface of the earth by a long shaft. Especially in the case ofnuclear explosions, it is important to prevent the escape of theradioactive by-products of the nuclear explosion. The force of the shockwave is countered by filling the access shaft with gravel or some othermaterial. However, this filling or stemming material is normally porousand will not prevent the escape of gases bearing radioactive materials.Thus, in addition to the gravel or other filling material, it isnecessary that there be a sealing material which will not allow gases toescape. The sealing material must be flexible so that it is notfractured by the shock Waves.

An important use of the sealing material of the present invention is inthe sealing of an access shaft to an underground explosion chamber. Atypical arrangement for an underground explosion includes a mined outchamber formed below the surface of the earth in which a nuclearexplosive is inserted. Various Wires or other sensing means are normallypresent in the chamber to monitor the results of the explosion. Thesewires are carried to the surface of the earth by means of insulatedcables. A vertical access shaft connects the explosion chamber with thesurface of the earth and provides a passage for the wires. In order toprevent the force of the explosion from being directed out the accessshaft, the access shaft is normally filled with gravel or similarmaterial to stem the shock wave. Since the gravel-type material isporous and thus will not prevent the escape of gases carryingradioactive materials, a sealant is necessary.

Normally, the sealant is placed in the access shaft with gravel bothabove and below it. Preferably, the height of the column of sealant isat least about 20 feet and may be as much as 200 feet. In sealing theaccess shaft, gravel is first put in place in the lower portion of theshaft. Then the unpolymerized sealant material is mixed and poured intothe shaft. The mixture at once begins to polymerize and after a givenamount of time will polymerize and crosslink to form the sealing gel.The gelling time is varied by varying the concentration of monomer,crosslinker and catalyst. After the sealant has polymerized, theremainder of the shaft may be filled up with gravel. At the time theunpolymerized sealant is introduced into the shaft, it has a sufiicientviscosity due to the presence of the filler material so that it does notdiffuse into the lower bed of gravel but instead stays in a confinedarea above the gravel be Another use of the sealing material of theinvention is filling voids in the wall around a missile silo. Themissile silo comprises a hole which has been drilled in the ground and asteel casing which is placed into the hole and bonded to the walls ofthe hole. Voids may be present in the formation and also between theformation and the cement. It is preferred that the material filling thevoids have a high electrical resistance so that it does not interferewith radio signals. To fill these voids, the flexible sealant of thepresent invention is introduced into the formation using conventionalgrouting techniques. If the pores into which the sealant is introducedare extremely fine, it may be necessary to eliminate the filler from thecomposition. Elimination of the filler will, of course, reduce theflexibilty and shock resistance of the sealant but the formation itselfwill function as a filler to some extent.

Another application of the flexible sealant is to form gaskets or beltsin the annulus between a well casing and the hole. The gaskets find usein wells wherein the casing is expected to move. Movement of the casingmay be caused by thermal expansion and contraction in a secondary steaminjection well in an oil field, because of high thermal stresses fromother sources, because of mechanical stresses, etc. The stress on thecasing is likely to break the brittle bond between the cement and theeasing. This will defeat one of the primary purposes of the cement, theprevention of water circulation up and down in the annular space betweenthe casing and the formation. When used in steam injection wells, directcontact of the sealant With steam should be avoided.

When gaskets or belts of flexible sealant are placed in the annulusbetween sections of conventional cement,

any water seepage will encounter the flexible sealant belt as the waterattempts to travel up and down the annular space. The bond between thecasing and the flexible sealant will not be broken due to theflexibility of the sealant and thus further migration of the water willbe prevented. Also, in the event that the sealant is broken, it willtend to swell in the water and effectively plug any water channels whichmight have existed.

The gaskets or belts of flexible sealant in the casingformation annulusmay be formed by introducing a volume of sealant between volumes ofcement during the cementing operation. The amount of sealant should besuch that it will form an annular belt about 5 to 1000 feet high andpreferably about 20 to 100 feet high.

The present invention may be more fully understood by reference to thefollowing examples.

EXAMPLE 1 A sealant composition was prepared by dissolving 9.5 grams ofacrylamide and 0.5 grams of N,N'-methylenebisacrylamide in 18 grams ofethylene glycol. To this solution was then added 72 grams of 99%glycerol. The initial viscosity of the composition was 160 centipoisesat 72 F. After 24 hours, the sealant was a clear, white gel having apenetrometer reading of 159, a flash point of 252 F. and a resistivityof approximately 1000 ohm meters.

EXAMPLE 2 TABLE I Colgate Gel N,N-methylene- 99% Ethylene timebiscrylamide glycerol glycol (min.)

1 Subsequent testing disclosed gel times of 3 to 190 minutes with thisparticular formulation.

It should be noted that wide variation in gel times occurs with the useof different grades of glycerol. The purity and water content of theglycerol is a partial determinant of the gel times.

EXAMPLE 3 The gel times for compositions containing various amounts ofsorbitol and glycerol using N,N'-methylenebisacrylamide and triallylphosphate as crosslinking agents were determined. Two basic mixingtechniques were used to produce the formulations set forth in Table IIhereinafter. In runs 1, 2, 4 and 7, the acrylamide and the crosslinkerswere dissolved in a polyol solution. In runs 3, 5, 6, 8 and 9, a onestep preparation was used in which acrylamide and the crosslinkers weredissolved in the polyol solution.

The premixture of 95% acrylamide and 5% N,N- methylenebisacrylamide wasused in all formations requiring the presence of both compounds.

The triallyl phosphate crosslinker was dissolved in the same operationas the monomer, but the triallyl phosphate and the monomer were alwaysadded separately to either diol or the polyol.

Sorbitol which is a solid at 75 F. was incorporated into formulations byusing either a commercially prepared 70% solution in water, or alaboratory prepared 50% solution in ethylene glycol. Thesorbitol-ethylene glycol solution was prepared by heating a mixture ofsolid sorbitol and liquid ethylene glycol in equal parts by weight ofthe two substances at 150 F. All components were 75 F. when the finalsealant formulations were prepared.

Table II below shows the results obtained. The amounts of materials aregiven in percent by weight. The curing temperature was 75 F. except forruns 8 and 9 in which the temperature was 120 F.

TABLE II Monomer, Diol Gel acryl- Qrossethylene time amide linker Polyolglycol (min.)

9. 0 a 1. 0 2 90 0 90 9.0 a 1.0 2 72 18 120 9.0 1.0 3 90 0 8.0 a 2.0 390 0 1 N,N-methylenebisacrylamlde. 2 Glycerol (Oolgate)99%.

I Sorbitol (Pfizer)70%.

t Greater than 24 hours.

6 50% sorbitol in ethylene glycol. I Triallyl phosphate.

It can be seen that the present invention is applicable to a widevariety of uses where a flexible sealant or grouting material isdesired. Furthermore, the composition of the sealant may be variedwidely within the guidelines set forth above. Thus, it should beunderstood that the above examples and description are merelyillustrative and should not be considered as limiting the scope of theinvention. The scope of the invention is limited only by the lawfulscope of the appended claims which follow.

I claim:

1. A flexible sealant composition comprising an acrylamide monomerexhibiting hydrogen bonding and having the structure wherein R is eitherH or CH R' is either H or an alkyl group and R" is either H or an alkylgroup, a polyfunctional crosslinking agent selected from the groupconsisting of N,N' methylenebisacryla'mide and triallyl phosphate, theamount of said polyfunctional crosslinking agent being from about 0.1%to about 10% based on the weight of said acrylamide, a diol selectedfrom the group consisting of ethylene glycol, diethylene glycol,triethylene glycol, polyethylene glycol, propylene glycol and 1,4-butene glycol, the weight ratio of said diol to said acrylamide beingfrom about 1:1 to about 5:1, and a polyol containing at least threehydroxy groups, the weight ratio of said polyol to said acrylamide beingfrom about 2:1 to about 20:1.

2. The composition of claim 1 wherein said monomer is acrylamide.

3. The composition of claim 1 wherein said crosslinking agent isN,N-methylenebisacrylamide.

4. The composition of claim 1 wherein said polyol is glycerol.

5. The composition of claim 1 wherein said diol is References Citedethylene glycol. t UNITED STATES PATENTS 6. The composmon of damn Iwherem the composi- 3 374 834 5/1968 Ramos et a1 6135 R tion includes afiller selected from the group consisting of silica, wood flour,bauxite, talc, scoria and mixtures 5 3511313 5/970 Elle et 166-295thereof. FOREIGN PATENTS 7. The composition of claim 6 wherein saidfiller is 222,316 6/1959 Australia 106 -287 SS silica.

8. The composition of claim 1 wherein said crosslink- ALLAN LIEBERMAN,Primary Examiner ing agent is triallyl phosphate. 10

9. The composition of claim 1 wherein said polyol is sorbitol. 61-36 R;166295; 26033.4 R, 41 A, 41 B, DIG 14

